1. Field of the Invention
The invention relates to the field of sensors. In particular the invention relates to sensors adapted for sensing in the area of interfaces involving biological, medical, chemical and physical processes.
2. Description of the Related Technology
Most physical, chemical and biological processes are surface driven. Biological processes and their outcomes are determined by the properties of the surfaces and interfacial areas of biological entities such as bones, membranes, cells, proteins, as well as their interaction with man-made materials such as polymers, metals (titanium, other), etc. Chemical processes involve formation of coatings such as suspensions, colloids, paints, corrosion protective layers, or catalytic processes, etc. Physical processes relate to gaseous, liquid and solid phase condensation, fabrication of thin films of various materials such as polymers, metals, metal oxides, crystals and polycrystals, (silicon, zinc oxide, etc,) or material modification via such processes as implantation, doping, etc. Typically, such interfacial areas exhibit nonuniform properties and consist of many different surfaces or sub-interfaces that form a multi-layered structure and/or different regions in the interfacial area.
FIGS. 1a-1b show a titanium implant 1 and bone 2 interface at various different levels of depth and layer thickness. FIG. 1a shows the interaction between the bone 2, the titanium implant 1 and bio-fluid 4 at the depth of roughly 1 μm from the bone/titanium interface. FIG. 1b shows the interaction between a titanium layer 1a and a titanium oxide layer 1b of the titanium implant 1 and the biofluid 4 at a depth of 1 nm from the bone/titanium interface. The interactions at different depths from the interface provide important information about what processes are going on between the titanium implant and the body. Similarly, in interfacial areas involving chemicals such as paints, one can distinguish several regions exhibiting different properties. In the case of physical processes, a typical example of an interfacial area having different layers or regions is a multi-layer structure of silicon material.
Therefore, in order to understand and monitor such processes as biocompatibility, drug interaction, cell-substrate interaction, tissue engineering, nanotechnology, absorption, and successfully design biological, medical, chemical and physical devices that are capable of addressing these needs, it is helpful to interrogate these surfaces and interfacial areas at different depths from the interface of interest, as shown in FIG. 2. Ideally, the interrogating method should be capable of providing information at different depths from an interface, or, in other words, slice interfacial areas at different depths. As a result of such an interrogation process, a map of the properties of individual layers or regions forming the interfacial area will be created. It is also advantageous to obtain information on the whole interfacial area as a result of the interrogation procedure.
Sensing mechanisms employed today do not typically seek to obtain information at different distances from the interface. A standard sensing mechanism will typically only try to detect the presence of certain objects and items using a single frequency (wavelength) and thus will obtain only a single information input for a specific portion of the interfacial area. Most sensors do not have the capability to interrogate the interfacial area at different distances from an interface or at different spatial resolutions.
Existing methods provide the means of interrogating in the area of an interface at only a single depth. Existing methods are based on optical, electrical and acoustical means, or sensing mechanisms. The optical methods utilize optical evanescent waves of a given frequency or wavelength. The typical frequency range of operation includes the visible range of optical waves which provide a depth of penetration on the order of 0.5-0.8 micrometers. An example of this single-depth optical technique for providing information about an interfacial area is surface plasmon resonance (SPR). Though SPR is used widely, it provides only limited information on interfacial processes. Electrical methods utilize a system of electrodes placed on the surface of the interrogating element, which subsequently is exposed to a detectable object. Here, the depth of penetration is on the order of tens of microns with very limited spatial resolution. Acoustic techniques utilize a single-depth. In all of these cases the depth of penetration is not a factor to be considered. Moreover, these processes do not provide resolutions in the nanometer range.
The techniques mentioned above do not have the ability to gather as much information as would be helpful to understand some complex processes, such as biocompatibility, drug interaction, cell-substrate interaction, tissue engineering, nanotechnology, absorption, and interactions with semiconductor devices (microchips). In order to better understand these and other systems involving non-uniform interfacial areas it is necessary to interrogate the interfacial area at different depths to obtain a more complete understanding of the processes that are taking place in the interfacial area.
Therefore, there exists a need for providing a more flexible and effective method and apparatus for interpreting and interrogating the interactions between different materials on a microscopic and nanoscopic scale.